The present invention relates to a process for forming low cost aluminum alloy hydroforms, particularly low cost hydroformed tubes suitable for assembly as automotive vehicle structures.
It is known to deform steel members such as steel tubes for forming automotive vehicle structures, by the process of hydroforming. It is also known that automotive vehicle structures formed of hydroformed steel members can provide advantages over vehicle structures formed according to alternative techniques, such as lowering vehicle weight, allowing component consolidation, improving vehicle performance and the like. Recently, there has been interest in using aluminum alloys for hydroformed automotive vehicle structures, particularly given that aluminum alloys provide an attractive high strength to weight alternative to hydroformed steel and because aluminum alloys are typically resistant to the corrosive environments also to which automotive vehicles are subjected. However, in view of metal forming needs quite often unique to aluminum alloys, the hydroforming of aluminum alloy components has tended to be expensive, labor intensive or both. Thus, there is a need for improved techniques for forming hydroformed aluminum vehicle structures, particularly hydroformed aluminum tubular structures wherein the techniques are more economical, less labor intensive or both.
The present invention meets these needs by providing an improved process for forming hydroformed aluminum members, with particular utility in the formation of tubular vehicle structures. According to the process, there is provided a molten aluminum alloy having no greater than about 6 weight percent magnesium. The molten aluminum alloy is dispensed substantially continuously to a twin belt continuous caster at a temperature of about 600xc2x0 C. to about 800xc2x0 C. Then the molten aluminum alloy is continuously cast with the twin belt caster into aluminum alloy strip material wherein the strip material has a gage thickness of about 10 millimeters to about 16 millimeters. Preferably, the strip material exits the caster at a temperature of about 400xc2x0 C. to about 600xc2x0 C. Thereafter, the aluminum alloy strip material is thinned to form aluminum alloy sheet material to a desired gage thickness of from about 2 millimeters to about 6 millimeters. The sheet material is formed into one or more aluminum alloy tubes while the sheet material remains at the desired gage thickness. The tubes are then hydroformed into the tubular automotive vehicle structure. Preferably, the tubular structure has at least one hydroformed contour and is a member of a frame of an automotive vehicle.